Nancy, for $4K, I'll come from Washington State, replumb your home, and then spend a couple of weeks enjoying the fall colors on the Northeast! You need to shop around for contractors. Copper replumbing of a mobile home is simple and should not cost anything like that. Sounds like the guy who quoted you $4K didn't want the job. Lots of plumbers only want new construction where they don't have to deal with the homeowner, clean-up, crawl under, or fit anything to existing pipe. One of the ways they avoid those jobs is to put an outlandishly high price on them. Others won't even submit a bid! Guess they have good reasons, but it makes it difficult for a homeowner to get a simple job done at a reasonable price. That's one reason many of us have turned to DIY.